Existing image sensors include a pixel unit array and a color filter unit array disposed over the pixel unit array. Each color filter unit in the color filter unit array covers a corresponding pixel unit. Each pixel unit includes a plurality of photosensitive pixels. In operation, the image sensors may be controlled to be exposed to light and output a merged image. The merged image includes a merged pixel array. The plurality of photosensitive pixels of a same pixel unit are merged into a merged photosensitive pixel for output. In this manner, a signal to noise ratio of the merged image can be increased. However, resolution of the merged image is decreased.